1. Field of the Invention
The present invention relates generally to a valve lifter for use in opening a valve of an engine such as an internal combustion engine
2. Description of the Related Art
Typically, internal combustion engines utilize a pair of intake and exhaust valves which are opened and closed synchronously due to the rotation of a cam shaft. It is known to construct valve trains for opening and closing the valves in such engines. Generally, a valve train includes a valve lifter which is placed adjacent a cam lobe on a cam shaft which is used to translate rotational motion of the cam shaft into axial motion of the valve. Typically, this is accomplished through a push rod and rocker arm assembly acting directly upon the valve. The valve is closed by a valve spring which biases the valve in a closed position.
One of the major sources of the frictional forces occurring in a driven valve train is the valve spring force required to counteract the inertia forces generated by the reciprocating mass, i.e., rocker arm, valve lifter, and push rod, and close the valve with adequate sealing. Conventionally, the valve lifter is made of a harden steel material which produces a relatively high reciprocating mass and valve spring force, thus limiting the maximum engine speed. Thus, there is a need in the art to reduce the reciprocating mass and valve spring force, correspondingly reducing the friction and increasing engine speed.
However, lightweight components typically have a low wear coefficient and normally include some sort of hard coating to increase their useful life. In the past, the peripheral surface of valve lifters have been coated with a hard material to prevent wear and increase the useful life of the lifter. While the coatings have increased the useful life of the valve lifter, they do not adequately reduce the coefficient of friction at the valve lifter/valve lifter guide interface. Thus, there is a need in the art to reduce the friction at the valve lifter and valve guide interface to increase the efficiency of the valve train, resulting in greater fuel economy of the engine.
Additionally, friction between the valve lifter and the cam lobe has been reduced through the use of a roller cam follower as opposed to a slider type follower. Typically, roller cam followers are mounted on needle bearings and in some instances have been journaled on a shaft. However, there is a need in the art to reduce the weight of roller cam followers.